//不要给我WA WA 叫
//一定AC
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <set>
#include <map>
#include <cstring>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include <iomanip>
#include <climits>
#define int long long 
#define x first 
#define y second 
using namespace std;
const int N = 1e5 + 10;
int a[N];
void solve()
{
    string s;
    cin >> s;
    if(isdigit(s[0])) 
    {
        cout << "No" << endl;
        return;
    }
    for(int i = 0; i < s.size(); i++)
    {
        if(isdigit(s[i]) == false && isalpha(s[i]) == false && s[i] != '_')
        {
            cout << "No" << endl;
            return;
        }
    }
    cout << "Yes" << endl;
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr),cout.tie(nullptr);
    int t = 1;
    while(t -- )  solve();
    return 0;
}
